Android多线程下载
2014-01-14 11:05
344 查看
一、多线程下载的原理、
将服务端的资源划分给成几个等分的块，分配给不同的线程同时执行下载。
划分方法 ：
每个线程分配的长度为：int blocksize = length/n
每个线程的起止位置（i-1）*blocksize--->i*blocksize-1
最后一个线程结束位置为length
二、步骤：
1、在客户端创建与服务端同等大小的文件，使用RandomAccessFile类远程文件的设置操作2.、开启几个线程，分配下载资源
3.、所有的线程执行完毕之后，文件下载完毕
三、java实现的多线程下载
1 package com.lewu.download;
2
3 import java.io.File;
4 import java.io.FileInputStream;
5 import java.io.FileOutputStream;
6 import java.io.InputStream;
7 import java.io.RandomAccessFile;
8 import java.net.HttpURLConnection;
9 import java.net.URL;
10
11 public class DownloadTest {
12 public static final String path = "http://192.168.1.118:8080/web/youdao.exe";
13 public static int threadcount = 0;
14
15 public static void main(String[] args) throws Exception {
16 // 1.在客户端端创建一个相同大小的文件（获取服务器文件的大小）
17
18 URL url = new URL(path);
19 HttpURLConnection conn = (HttpURLConnection) url.openConnection();
20 conn.setRequestMethod("GET");
21 conn.setConnectTimeout(5000);
22 conn.setRequestProperty(
23 "User-Agent",
24 "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
25 int length = conn.getContentLength();
26 System.err.println("文件的长度为"+length);
27 File file = new File("youdao.exe");
28 RandomAccessFile randomfile = new RandomAccessFile(file, "rwd");
29 randomfile.setLength(length);
30
31 // 创建三个线程 :线程分配下载资源
32 int blocksize = length / 3;
33 for (int i = 1; i <=3; i++) {
34 // 线程执行下载操作 ，需要定位下载的位置，则需要设置一些参数
35 int beginsize = (i - 1) * blocksize;
36 int endsize = i * blocksize - 1;
37 if (i == 3) {
38 endsize = length;
39 }
40 int id = i;
41
42 // 启动线程
43 new Thread(new DownloadThread(id, beginsize, endsize)).start();
44 }
45
46 }
47
48 static class DownloadThread implements Runnable {
49
50 private int id;
51 private int beginsize;
52 private int endsize;
53
54 public DownloadThread(int id, int beginsize, int endsize) {
55 this.id = id;
56 this.beginsize = beginsize;
57 this.endsize = endsize;
58 }
59
60 @Override
61 public void run() {
62 try {
63 // 每一个线程在创建的时候 都创建一个名为id.text的文件用来保存下载进度
64 File idfile = new File("" + id + ".txt");
65 if (idfile.exists()) {
66 // 将内容即进度读取出来
67 FileInputStream fin = new FileInputStream(idfile);
68 byte[] result = StreamTools.getBytes(fin);
69 String strinfo = new String(result);
70 if (!"".equals(strinfo) && strinfo != null) {
71 beginsize = Integer.parseInt(strinfo);
72 }
73 }
74 URL url = new URL(DownloadTest.path);
75 HttpURLConnection conn = (HttpURLConnection) url
76 .openConnection();
77
78 conn.setRequestMethod("GET");
79 conn.setConnectTimeout(5000);
80 if (beginsize > endsize) {
81 beginsize = endsize - 1;
82 }
83 conn.setRequestProperty(
84 "User-Agent",
85 "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
86 conn.setRequestProperty("Range", "bytes=" + beginsize + "-"
87 + endsize);
88 System.out.println("线程"+id+"从" + beginsize + "开始下载" + endsize + "结束");
89
90 File file = new File("youdao.exe");
91 RandomAccessFile randomfile = new RandomAccessFile(file, "rwd");
92 // 如果下载被强行中断，这保存下载的位置，
93 randomfile.seek(beginsize);
94
95 InputStream in = conn.getInputStream();
96 byte[] bt = new byte[1024];
97
98 int len = 0;
99 int total = 0;
100 while ((len = in.read(bt)) != -1) {
101 randomfile.write(bt, 0, len);
102 // 下载量 下载位置
103 total += len;
104 // 将位置信息保存到相应的文件
105 FileOutputStream out = new FileOutputStream(idfile);
106 out.write((beginsize + total + "").getBytes());
107 out.flush();
108 out.close();
109
110 }
111 in.close();
112 randomfile.close();
113 System.out.println("线程" + id + "执行完毕！");
114
115 // 使用synchronized的代码块保count被多个线程同时访问
116 synchronized (DownloadTest.class) {
117 DownloadTest.threadcount++;
118 if (DownloadTest.threadcount >= 3) {
119 System.out.println("所有的线程都执行完毕了");
120 for (int i = 0; i < 3; i++) {
121 File deleteFile = new File(i + ".txt");
122 System.out.println(i + "删除" + deleteFile.delete());
123 }
124 }
125
126 }
127
128 } catch (Exception e) {
129 e.printStackTrace();
130 }
131 }
132 }
133 }四、移植到Android上
功能：1、界面上有下载进度条，可以记录下载进度2、设置暂停按钮（通过设置flag控制）
1 package com.lewu.download;
2
3 import java.io.File;
4 import java.io.FileInputStream;
5 import java.io.FileOutputStream;
6 import java.io.InputStream;
7 import java.io.RandomAccessFile;
8 import java.net.HttpURLConnection;
9 import java.net.URL;
10 import android.app.Activity;
11 import android.os.Bundle;
12 import android.os.Environment;
13 import android.view.View;
14 import android.view.View.OnClickListener;
15 import android.widget.Button;
16 import android.widget.EditText;
17 import android.widget.ProgressBar;
18 import android.widget.Toast;
19
20 public class MutiDownloadAndActivity extends Activity implements
21 OnClickListener {
22 private EditText down_edit;
23 private Button down_sure;
24 private Button down_stop;
25 private ProgressBar bar;
26 private int totalsize;
27 private boolean flag=true;
28 public static int threadcount = 0;
29
30 @Override
31 public void onCreate(Bundle savedInstanceState) {
32 super.onCreate(savedInstanceState);
33 setContentView(R.layout.main);
34
35 down_edit = (EditText) findViewById(R.id.down_edit);
36 down_sure = (Button) findViewById(R.id.down_sure);
37 down_stop = (Button) findViewById(R.id.down_stop);
38 bar = (ProgressBar) findViewById(R.id.progressBar1);
39
40 down_sure.setOnClickListener(this);
41 down_stop.setOnClickListener(this);
42
43 }
44
45 @Override
46 public void onClick(View v) {
47 switch (v.getId()) {
48 case R.id.down_sure:
49
50 String path = down_edit.getText().toString().trim();
51 System.out.println(path + ">>>>>>>>>>");
52 if ("".equals(path)) {
53 Toast.makeText(this, "路径不能为空", 0);
54 return;
55 } else {
56 down_stop.setClickable(true);
57 down_stop.setEnabled(true);
58 try {
59 URL url = new URL(path);
60 HttpURLConnection conn = (HttpURLConnection) url
61 .openConnection();
62 conn.setRequestMethod("GET");
63 conn.setConnectTimeout(5000);
64 conn.setRequestProperty(
65 "User-Agent",
66 "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
67 int length = conn.getContentLength();
68 System.err.println("文件的长度为" + length);
69 //设置进度条的进度
70 bar.setMax(length);
71 File file = new File(
72 Environment.getExternalStorageDirectory(),
73 getFileName(path));
74 RandomAccessFile randomfile = new RandomAccessFile(file,
75 "rwd");
76 randomfile.setLength(length);
77
78 // 创建三个线程 :线程分配下载资源
79 int blocksize = length / 3;
80 for (int i = 1; i <= 3; i++) {
81 // 线程执行下载操作 ，需要定位下载的位置，则需要设置一些参数
82 int beginsize = (i - 1) * blocksize;
83 int endsize = i * blocksize - 1;
84 if (i == 3) {
85 endsize = length;
86 }
87 int id = i;
88
89 // 启动线程
90 new Thread(new DownloadThread(id, beginsize, endsize,
91 path)).start();
92
93 }
94 } catch (Exception e) {
95 e.printStackTrace();
96 }
97 break;
98 }
99
100 case R.id.down_stop:
101 flag = false;
102 down_stop.setClickable(true);
103 down_stop.setEnabled(true);
104
105 break;
106
107 }
108 }
109
110 class DownloadThread implements Runnable {
111
112 private int id;
113 private int beginsize;
114 private int endsize;
115 private String path;
116
117 public DownloadThread(int id, int beginsize, int endsize, String path) {
118 this.id = id;
119 this.beginsize = beginsize;
120 this.endsize = endsize;
121 this.path = path;
122 }
123
124 @Override
125 public void run() {
126 try {
127 flag = true;
128 // 每一个线程在创建的时候 都创建一个名为id.text的文件用来保存下载进度
129 File idfile = new File("/mnt/sdcard/" + id + ".txt");
130 if (idfile.exists()) {
131 // 将内容即进度读取出来
132 FileInputStream fin = new FileInputStream(idfile);
133 byte[] result = StreamTools.getBytes(fin);
134 String strinfo = new String(result);
135 if (!"".equals(strinfo) && strinfo != null) {
136 beginsize = Integer.parseInt(strinfo);
137 }
138 }
139 URL url = new URL(path);
140 HttpURLConnection conn = (HttpURLConnection) url
141 .openConnection();
142
143 conn.setRequestMethod("GET");
144 conn.setConnectTimeout(5000);
145 if (beginsize > endsize) {
146 beginsize = endsize - 1;
147 }
148 conn.setRequestProperty(
149 "User-Agent",
150 "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; .NET CLR 2.0.50727)");
151 conn.setRequestProperty("Range", "bytes=" + beginsize + "-"
152 + endsize);
153 System.out.println("线程" + id + "从" + beginsize + "开始下载"
154 + endsize + "结束");
155
156 File file = new File(Environment.getExternalStorageDirectory(),
157 getFileName(path));
158 RandomAccessFile randomfile = new RandomAccessFile(file, "rwd");
159 // 如果下载被强行中断，这保存下载的位置，
160 randomfile.seek(beginsize);
161
162 InputStream in = conn.getInputStream();
163 byte[] bt = new byte[1024];
164
165 int len = 0;
166 int total = 0;
167 while ((len = in.read(bt)) != -1) {
168 randomfile.write(bt, 0, len);
169 // 下载量 下载位置
170 total += len;
171
172 // 设置进度条的进度
173 setProgressbarProgress(len);
174
175 // 将位置信息保存到相应的文件
176 FileOutputStream out = new FileOutputStream(idfile);
177 out.write((beginsize + total + "").getBytes());
178 out.flush();
179 out.close();
180 if(!flag){
181 return;
182 }
183
184 }
185 in.close();
186 randomfile.close();
187 System.out.println("线程" + id + "执行完毕！");
188
189 // 使用synchronized的代码块保count被多个线程同时访问
190 synchronized (MutiDownloadAndActivity.class) {
191 MutiDownloadAndActivity.threadcount++;
192 if (MutiDownloadAndActivity.threadcount >= 3) {
193 System.out.println("所有的线程都执行完毕了");
194 for (int i = 1; i <= 3; i++) {
195 File deleteFile = new File("/mnt/sdcard/" + i
196 + ".txt");
197 System.out.println(i + "删除" + deleteFile.delete());
198 }
199 }
200
201 }
202
203 } catch (Exception e) {
204 e.printStackTrace();
205 }
206 }
207 }
208
209 public static String getFileName(String path) {
210 int index = path.lastIndexOf("/") + 1;
211 return path.substring(index);
212
213 }
214
215 public void setProgressbarProgress(int len) {
216 if (len != 0) {
217 totalsize += len;
218 bar.setProgress(totalsize);
219 }
220
221 }
222
223 }下载界面：
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